fec: refactor init function

fec_enet_init() does the hardware initialisation and then calls
fec_restart() which does the same initialisation again, so we
can safely remove the initialisation from fec_enet_init().

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>